<html>
<head>
    <style>
        body {
            display: flex;
            justify-content: center;
            align-items: center;
            height: 100vh;
            background: #000;
        }

        *, *::before, *::after {
            box-sizing: border-box;
        }

        @keyframes rotate {
            100% {
                transform: rotate(1turn);
            }
        }

        .conic {
            position: relative;
            z-index: 0;
            width: 400px;
            height: 300px;
            margin: 20px;
            border-radius: 10px;
            overflow: hidden;
            padding: 2rem;}

        .conic::before {
             content: '';
             position: absolute;
             z-index: -2;
             left: -50%;
             top: -50%;
             width: 200%;
             height: 200%;
             background-color: #1a232a;
             background-repeat: no-repeat;
             background-position: 0 0;
             background-image: conic-gradient(transparent, rgba(168, 239, 255, 1), transparent 30%);
             animation: rotate 4s linear infinite;
         }

        .conic::after {
             content: '';
             position: absolute;
             z-index: -1;
             left: 6px;
             top: 6px;
             width: calc(100% - 12px);
             height: calc(100% - 12px);
             background: #000;
             border-radius: 5px;
         }
        }

        .conic-demo::after {
            animation: opacityChange 5s infinite linear;
        }

        @keyframes opacityChange {
            50% {
                opacity:.5;
            }
            100% {
                opacity: 1;
            }
        }
    </style>
</head>
<body>
<div class="conic"></div>
<div class="conic conic-demo"></div>
</body>
</html>
